The CRISPR-Cas9 complex (in blue and yellow) is able to precisely cut DNA (in red).
Credit: Alfred Pasieka/Science Photo Library
In a small-scale clinical trial, a research team has discovered that a gene-editing technique known as CRISPR can be used to modify immune cells so that they recognize mutated proteins in each patient’s tumor. These cells are then safely released into the patient’s body to search for and destroy the target tumor.
This trial is the first attempt to reconcile two critical areas of cancer research: the use of gene editing to tailor therapies to individual patients, and the engineering of T-cell immune cells by genetically modifying them to better target tumors. The researchers tested the effectiveness of this methodology in 16 patients with solid tumors, including tumors of the breast and colon.
In this regard, Anthony Ribas, a physician and researcher specializing in cancer diseases from the University of California, Los Angeles, who participated in the study, said, “This is probably the most complex clinical treatment that we have ever tried, as we are trying to mobilize an army of T cells in the patient.” .
The results of this research work have been published in a journal Nature (SP Foy et al. Nature https://doi.org/jk4f; 2022) It was presented last November 10 at the Society for Immunotherapy of Cancer meeting in Boston, Massachusetts, USA.
Ribas and his research team began their experiment by sequencing DNA in blood samples and tumor biopsies, looking for mutations that appear in tumors rather than in the blood. The researchers had to repeat this step for each patient who participated in the trial. “The mutations in each type of cancer are different, and although there are common mutations between types of cancer, there are few,” Ribas comments.
Next, the research team used algorithms to predict which mutations were most likely to trigger a response from T cells, which are white blood cells that scour the body for any cells that exhibit abnormal behavior. About this, says Stephanie Mandel, chief scientific officer of PACT Pharma, in South San Francisco, California, USA, and the principal investigator of the study: “If you discover [الخلايا التائيّة] Anything that looks abnormal in the body, it kills it. But in the cancer patients we see clinically, their immune systems lose their battle at some point, and the cancerous tumor grows.”
From here, after the research team conducted a series of analytical examinations with the aim of validating its expectations and the results it reached, as well as designing protein receptors capable of detecting tumor mutations, it drew blood samples from each participant in the experiment, and used the “CRISPR” technology to insert genes. that encode these receptors to the T cells present in those samples. After that, all the participants in the experiment had to take a drug that reduces the numbers of immune cells forming in their bodies, before injecting them with the engineered T cells.
“This is an incredibly complex manufacturing process,” says Joseph Fraita, a researcher who specializes in designing T-cell-based therapies from the University of Pennsylvania in Philadelphia, and in some cases the whole process took more than a year. .
Each of the 16 participants received engineered T cells targeting up to three different targets. Next, the researchers detected the engineered cells in the participants’ blood samples, found near tumors in higher concentrations than the unengineered T cells before treatment began. After one month of treatment, five of the participants were stable, meaning their cancers had not progressed, and only two had side effects, which the researchers suggested were due to the activity of the engineered T cells.
Ribas believes that although the treatment’s efficacy has been shown to be low, the researchers used relatively small doses of T cells to demonstrate the safety of this approach. “Next time, we’ll just have to give stronger doses.”
As researchers continue to pursue ways to accelerate the development of these therapeutic approaches, it is expected that the engineered cells will have a shorter lifespan in cell cultures and become more effective when injected into the body. This is what Frattata preaches: “The technology will get better and better.”
strong start
The use of engineered T cells – known as chimeric antigen-receptor-producing T cells (CAR T) cells – had been used to treat some types of leukemia and lymphoma, but solid tumors in particular remained incurable at the time. CAR T cells are only active against proteins expressed on tumor cell surfaces, while many types of blood cell tumors and lymphomas co-produce these proteins, obviating the need to design new receptors that match T cells for each patient.
However, Fraita says, no proteins have been discovered that are involved in the production of solid surfaces of tumors. Solid tumors also present a physical barrier to T cells, which must travel through the blood to the tumor and then penetrate it to kill cancer cells. In addition, tumor cells sometimes suppress immune responses by releasing inhibitory chemical signals and depleting the body’s local stores of nutrients to fuel their rapid spread.
“The environment around the tumor is like a cesspool that T cells infiltrate, which in turn lose part of their effectiveness once they reach the focus of the tumor,” Fraetta explains.
Building on this proof of concept, Mandel and her research team hoped to be able to engineer T cells that could not only detect cancerous mutations, but also become more effective near tumors. Mandel sees several promising ways to enhance the effectiveness of T cells, such as removing receptors that respond to tumor immunosuppressive signals, or modifying metabolic activity so that it is easier for these T cells to secure an energy source within the tumor environment.
Avri Bossi, a researcher in the field of cell and gene therapies for cancer from the University of Pennsylvania, says that such complex designs could become very effective, thanks to recent technical advances in the use of CRISPR to edit T cells in the embryo. “This method has achieved amazing efficiency, and I expect that in the next decade we will see highly advanced means of engineering immune cells,” Bossi adds.